Atomic force microscopy (AFM) has emerged as a promising tool to characterize the mechanical properties of biological materials and cells. In our studies, undifferentiated and early differentiating mouse embryonic stem cells (mESCs) were assessed individually using an AFM system to determine if we could detect changes in their mechanical properties by surface probing. Probes with pyramidal and spherical tips were assessed, as were different analytical models for evaluating the data. The combination of AFM probing with a spherical tip and analysis using the Hertz model provided the best fit to the experimental data obtained and thus provided the best approximation of the elastic modulus. Our results showed that after only 6 days of differentiation, individual cell stiffness increased significantly with early differentiating mESCs having an elastic modulus two-to threefold higher than undifferentiated mESCs, regardless of cell line (R1 or D3 mESCs) or treatment. Singletouch (indentation) probing of individual cells is minimally invasive compared to other techniques. Therefore, this method of mechanical phenotyping should prove to be a valuable tool in the development of improved methods of identification and targeted cellular differentiation of embryonic, adult, and induced-pluripotent stem cells for therapeutic and diagnostic purposes.

This article presents a review on the existing techniques for manipulating biological cells. Because biomanipulation involves a wide range of disciplines, from biology to engineering, we concentrate on some of the key methodologies that would result in an efficient biomanipulation system. Some of the key methodologies discussed in this article for cell manipulation relate to the use of magnetics, microelectromechanical systems (MEMS)-based approaches, optics, electric field, and mechanical techniques. Recent advances in engineering have allowed researchers worldwide to address the problems arising from conventional manipulation techniques. This paper assimilates significance and limitations of biomanipulation techniques described in the literature.

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International audienceIn order to understand and characterize the mechanical property and response of the mouse embryonic stem cells (mESC), we used an atomic force microscope (AFM) combined with a PHANToM haptic feedback device. Atomic force microscopy has rapidly become a valuable tool for quantifying the biophysical properties of single cells or a collection of cells through force measurements. We report herein the mechanical characterization of single mESC using indentation-relaxation measurements with micro-sphere AFM probes for fixed and live undifferentiated mESC. During cell indentation for both live and fixed undifferentiated cells, we provided force feedback to the user in real-time through the PHANToM haptic feedback device as the AFM tip was deforming the cell. The force was amplified for the human operator to perceive the change in force during cell indentation by the AFM cantilever. This information can be used as a mechanical marker to characterize state of the cell (live and fixed). As the interpretation of atomic force microscopy-based indentation tests is highly dependent on the use of an appropriate theoretical model of the testing configuration, various contact models are presented to predict the mechanical behavior of an individual mouse embryonic stem cells (mESC) in different states. A comparison study with finite element simulations (FEM) of spherical tip indentation demonstrates the effectiveness of our computational model to predict the mESC deformation during indentation and relaxation nanomanipulation tasks